HVAC Lecture, heating, ventilation, and air conditioning

1. THERMAL INSULATION
June 5th, 2017 Lecture 7 Ephrem M.

2. The polar bear has a thick
body fur to insulate himself
from the chilly environment
around. Eskimo lends this fur
to keep his body warm, which
will be in stark contrast with
the surrounding.
A casual observation around clearly shows why women are less panicky
when it comes to handling hot things; it is because of their insulating
subcutaneous fat. The equivalent analogy on this biological systems is
the insulation of buildings from their natural setting.
THERMAL INSULATION

3. The sheathing often placed around steam
and hot-water pipes, for instance, reduces
heat loss to the surroundings, and
insulation placed in the walls of a
refrigerator reduces heat flow into the unit
and permits it to stay cold.
THERMAL INSULATION
Apart from geometrically responding to a harsh climate by manipulating the
form, insulation of buildings from the environment is a wise insight in energy
conscious world of the day.
Thermal insulating materials are used to reduce the flow of heat between hot
and cold regions.

4. What is Thermal Insulation?
Where there is difference in temperature of inside of a building and
outside atmosphere, heat transfer takes place from areas of higher
temperature to lower temperature. When the external temperature is
low, the internal temperature should be high so as to produce
thermal comfort.
Thermal insulation indicates the construction or provisions by way of
which transmission of heat from or in the room is retarded.
Thermal insulation can be attained during the design process from
providing thermal insulating materials on the “shell” of the building.

5. General methods of Thermal Insulation
1. heat insulation by orientation
2. Heat insulation by shading
3. Heat insulation by proper height of
ceiling

6. General methods of Thermal Insulation
1. heat insulation by orientation
2. Heat insulation by shading
3. Heat insulation by proper height of ceiling
1. internal building
surfaces which can
receive direct incident
solar radiation from
winter to summer
2. Optimum inclination
of solar cells for global
radiation throughout the
year
the orientation of the building with respect to
the sun has a very important bearing on its
thermal behaviour. For optimum orientation,
there are usually conflicting requirements.
Minimum transfer of solar heat desired during
the day in summer, while maximum heating of
rooms by solar heat is required during winter.

7. 1. heat insulation by orientation
2. Heat insulation by shading
3. Heat insulation by proper height of ceiling
Shading of roof brings down the surface temperature,
but it is very difficult to achieve this effect in practice,
especially when the altitude angle of the sun is high
during the peak heat gains in the afternoon, between
1100h and 1500h.
Raising the parapet walls can help only when the altitude
angle of the sun is low.
General methods of Thermal Insulation

8. 1. heat insulation by orientation
2. Heat insulation by shading
3. Heat insulation by proper height of ceiling
While the surface temperature of the ceiling does not
vary with its height, the intensity of the long wave
radiation, emitted by the ceiling decreases as it
travels downwards. The effect of vertical gradient of
radiation intensity is not significant beyond 1 to 3m.
Hence it should be adequate to provide ceiling at a
height of about 1 to 1.3m above the occupant.
General methods of Thermal Insulation

9. Advantages of Thermal Insulation
✓It provides comfort as it keeps room:
▪ cool in summer and
▪ hot in winter.
✓It saves fuel by minimizing heat transfer,
✓prevents condensation or moisture deposition on interior
walls and ceilings and
✓it prevents freezing of water taps in extreme winter, and
heat loss in case of hot water system.

10. Thermal Insulation functions
1. reduce thermal conduction in the material in which heat is
transferred by electrons;
2. reduce thermal convection current, which can be set up
in air- or liquid-filled spaces
3. reduce radiation heat transfer in which thermal energy is
transported by electromagnetic waves.

11. Thermal Insulation functions
Conduction and convection are suppressed in a vacuum, in which
radiation is the only method of transferring heat.
If the surfaces are made highly reflective, radiation can also be
reduced.
Thus, thin aluminium foil can be used in building walls, and
reflecting metal on roofs minimizes the heating effect of the Sun.

12. Thermal Insulation functions
Air offers about 15,000 times as much resistance to heat flow
as a good thermal conductor such as silver does, and about 30
times as much as glass.
Typical insulating materials, therefore, are usually made of non-
metallic materials and are filled with small air pockets.
They include magnesium carbonate, cork, felt, cotton batting,
glass wool, and diatomaceous earth.

13. Thermal Insulation functions

14. Thermal Insulation functions
In building materials, air pockets provide additional insulation in
hollow glass bricks, double-glazed windows (consisting of two or
three sealed glass panes with a thin air space between them),
and partially hollow concrete tile.
Insulating properties become poorer if the air space becomes
large enough to allow thermal convection, or if moisture seeps in
and acts as a conductor.

15. Thermal Insulation functions
Home-heating and air-conditioning costs can be reduced by proper
building insulation.
In cold climates about 8cm (about 3in) of wall insulation and about 15
to 23cm (about 6 to 9in) of ceiling insulation are recommended.
Super insulation has recently been developed, primarily for use in
space, where protection is needed against external temperatures near
absolute zero.
Super insulation fabric consists of multiple sheets of aluminized Mylar,
each about 0.005cm (0.002in) thick, separated by thin spacers, with
about 20 to 40 layers per cm (50 to 100 layers per in).

16. Thermal Insulation functions

17. Thermal Insulation functions
1. Low temperatures: insulation for vessels containing cryogenic
materials, such as liquefied natural gas
2. Ambient temperature: insulation for building structures
3. Medium temperature: insulation for tanks, pipes, and equipment in
industrial process heat applications
4. High temperatures: refectory or other specialized insulation materials
used in foundry work, nuclear power facilities, the aerospace industry
Thermal insulation controls heat flow under temperatures ranging from absolute zero to 3000oF
(1600oC). This broad range can be subdivided into four general temperature regimes that classify
applications for various types of insulation;

18. Three points to consider in using
Thermal Insulating Materials
 Where is thermal insulation used?
 How does insulation work?
 What is the R-value (Thermal resistivity)?

19. Use of thermal insulation
If the air outside is cold, you may want to protect your skin by wearing clothes
that keep the cold out and the body warmth in.
If your house has cool air inside during the summer, you may want to prevent
the temperature from becoming the same as the hot air outside by having the
house well insulated.
You may want to prevent hot drink from becoming room temperature by putting
it in a thermos bottle.
Three points to consider in using
Thermal Insulating Materials

20. How Does Insulation Work?
Three points to consider in using
Thermal Insulating Materials
Insulation is a barrier that minimizes the transfer of heat energy from
one material to another by reducing the conduction, convection and/or
radiation effects.
Most insulation is used to prevent the conduction of heat.
Less dense materials are better insulators.
Thus, gases insulate better than liquids.

21. How Does Insulation Work?
Conduction occurs when materials--especially solids--are in
direct contact with each other.
To slow down the transfer of heat by conduction from one
solid to another, fiberglass and vacuum are mostly used.
Insulation from conduction
Three points to consider in using
Thermal Insulating Materials

22. How Does Insulation Work?
Radiation is transfer of heat from warm objects by
radiating infrared electromagnetic waves which can be
prevented by a shiny material to prevent radiation heat
transfer.
Insulation from Radiation
Three points to consider in using
Thermal Insulating Materials

23. R-Value
The R-value of a material is its resistance to heat flow and is an indication of its
ability to insulate.
• It is used as a standard way of telling how good a material will insulate.
• The higher the R-value, the better the insulation.
Its units of measurement:
▪ (square feet x hour x degree F)/BTU in the English system
▪ (square meters x degrees C)/watts in the metric system
Three points to consider in using
Thermal Insulating Materials

24. R-Value
Three points to consider in using
Thermal Insulating Materials
Material R-Value Material R-Value
Hardwood siding (1 in. Thick) 0.91 Cellulose fibre (1 in. Thick) 3.7
Wood Shingles (lapped) 0.87 Flat glass (0.125 in. Thick) 0.89
Brick (4 in. Thick) 4 Insulating glass (0.25 in space) 1.54
Concrete block (filled cores) 1.93 Air space (3.5 in. thick) 1.01
Fiberglass batting (3.5 in. Thick) 10.9 Free tagnant air layer 0.17
Fiberglass batting (6 in. Thick) 18.8 Drywall (0.5 in. Thick) 0.45
Fiberglass board (1 in. Thick) 4.35 Sheathing (0.5 in. Thick) 1.32

25. Thermal Insulating Materials
1. slab or block insulation—known as blocks or boards, 2.5cm thick and 60cm x
120cm or more in area. These may be made of cork board, mineral wool,
vermiculite, cellular glass, cellular rubber, saw dust, asbestos cement, etc. these
are fixed to walls, slabs or roofs.
slab or block insulation

26. Thermal Insulating Materials
slab or block insulation

27. Thermal Insulating Materials
2. Blanket insulation—these are flexible fibrous rolls made from mineral wool,
processed wood fibres, cotton, animal hair, etc. available in thickness of 12 to
80mm. These are directly spread on the wall or ceiling surfaces.

28. Thermal Insulating Materials
3. Loose fill insulation—may
consist of fibrous materials like
rock wool, slag wool, cellulose
or wood fiber wool, etc. filled
loosely in the studding space.

29. Thermal Insulating Materials
4. Batt insulation—similar to blanket insulations except that these are small in size
but of greater thickness. These are also spread on surface of walls and ceiling.
Batt insulation

30. Thermal Insulating Materials
5. Insulating board—used
for interior lining of walls
and also for partition
walls, available in
different sizes and
thickness
6. Light weight aggregate—heat resistance of concrete can
be greatly increased by using blast furnace slag, burnt
clay, vermiculite

31. Thermal Insulating Materials
7. Reflective sheet—have high
reflectivity and low emissivity, thus
offering high heat resistance. It
consist of gypsum boards, steel
sheet, aluminium foils, etc.
Unlike others, reflective sheets rely on
their surface characteristics, thickness
of air space & temperature differences
for their insulating value.

32. Thermal Insulating Materials
8. Air barrier—effectively retard or
stop the flow of warm, moisture-
laden air from inside a building
outward through walls, ceiling, and
floors to the colder, dryer outside
atmosphere.

33. Application of Insulation materials
1. Flexible insulation – provided in open spaces
in the wall, ceiling, or roof construction
where it will not be subjected to loads, as it
is easily compressible.
Quilts or blankets are put between furring strips
on masonry wall. Blanket insulation divides the
space into two or more air spaces.
For greater efficiency, the insulation is fastened at the sides and ends so that
there will be no air leakage between spaces. Batts are placed between studs

34. 2. Fill insulation - installed by pouring the loose granulated material into
open spaces between the studs or between ceiling joists. The material
may be blown into place through large flexible tubes employing low air
pressure. Care is taken to insure the complete filling of space between
stud.
Application of Insulation materials

35. 3. Reflective insulation - fixed
between studs, joists or rafter.
It is held more tightly by using
nailing strips. This type of
insulation divides the space into
two or more air spaces. It is
essential that the insulation is
fastened at the sides, top,
bottom and all laps to restrict
the air circulation between the
two spaces.
Application of Insulation materials

36. Choice of Insulating materials
The choice of insulating material depends upon:
➢the cost of material,
➢area to be covered,
➢standard of insulation required and
➢coat of heating and cooling.

37. Properties of Insulating materials
✓high thermal resistance,
✓reasonably fireproof,
✓insect proof,
✓durable,
✓non-absorbent of moisture,
✓cheaper and readily available.
The insulating material Should have properties of:
It should be noted that low
density insulating material give
better insulations than high
density materials. Also the
presence of air spaces in the
insulating material increases
thermal insulation while presence
of moisture decreases thermal
insulation.